By Nick Collins, Science Correspondent 7:00AM BST 08 Sep 2012
Every family has one: at the climax of a gripping murder mystery the same know-it-all will declare smugly, “I knew the culprit all along”.
Now it is the braggarts’ turn to be found out. Scientists claim to have established that, far from being super-sleuths, such people are usually deluded.
Researchers found that they are suffering from “hindsight bias”, when a person genuinely believes that they know something when in fact they are hearing or seeing it for the first time.
Although the effects might seem relatively harmless, researchers claimed it could prevent people learning why something has happened or from taking advice.
Prof Neal Roese, of Northwestern University in Chicago, said: “If you feel like you knew it all along, it means you won’t stop to examine why something really happened.
“It’s often hard to convince seasoned decision-makers that they might fall prey to hindsight bias.”
A study by Prof Roese and Dr Kathleen Vohs found three different tricks of the mind that can fool the brain in this way.
Firstly, a person’s memory can become distorted after an event which they had discussed beforehand, tricking them into thinking they knew the outcome before it began.
For example, a group of friends may discuss a colleague whom they find suspicious and then discover they are caught embezzling funds from the company. One of the friends may later believe
that they predicted their colleague would get caught because it follows the same vein as their discussion, even if fraud had not been mentioned, the researchers said.
A second trick occurs when something seems so inevitable in hindsight that people believe they must have known it would happen all along.
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